The GlobICE adventure and beyond...

By On ·

Background

As described on the GlobICE website (cheers Alan Muir), this ambitious project lead by UCL started in September 2005 and is a part of European Space Ageny's (ESA) Data User Element (DUE) of the Earth Observation Envelope Programme. The main purpose of GlobICE is to define, implement and validate a sea ice information system to support the World Climate Research Programme Climate and Cryosphere project (CliC) with validated sea ice motion, deformation and flux products derived from SAR data in the ESA archive. A key objective of the CliC programme is to improve the representation, in global climate models, of interactions between sea ice, the oceans and the atmosphere.

Left: Envisat ASAR WS mode coverage for the 3 day period of 16-18 MArch 2008. Right: typical spatial coverage is shown as the Annual % days that can be tracked. This map is deduced from the frequency of overlapping ASAR pairs.

The GlobICE project is based on the heritage provided by the RADARSAT Geophysical Processor System (RGPS) to obtain high-resolution ice displacement from repeat Synthetic Aperture Radar (SAR) imagery [Kwok1990]. The project was specifically designed to exploit the large archive of SAR data over sea ice currently held by ESA. Following processor prototyping and a study of SAR data coverage it was decided that GlobICE products would only be processed from ENVISAT ASAR data (see figure on the left), and not from ERS-1 or ERS-2 SAR data which has a lower 100km swath width and repeat cycle making it unsuitable for the wide area and seasonal sea-ice tracking required. The ice displacement, which is determined at intervals of a few days, allows the subsequent generation of a number of different high resolution products useful for climate research including Eulerian and Lagrangian motion, Ice deformation, Open water fraction and Gateway mass flux.

Comparison with NASA's RGPS and with model predictions


In parallel to the main goal of my first project at CPOM that consisted in introducing a new anisotropic rheology in the Los Alamos climate code CICE, I have collaborated with the remote sensing group based in the Department of Earth Sciences at University College London (UCL). I have produced one of the first animations of the Arctic sea ice dynamics based on the GLOBICE product. I have also contributed to the GLOBICE validation campaign, produced a comparative study of the new ESA GLOBICE project with NASA's well established RGPS project and showed that the two projects can complement each other (see figure on the right) to offer a more complete picture and an extended coverage of the sea ice dynamics over the Arctic at length scale down to 5 km. The GlobICE products offer a valuable data set against which climate model can be validated. It has been shown [Rampal2011] that models fail to capture the accelerating sea ice dynamics over recent decades. In addition even the statistical distributions of the deformation rate of the ice is inadequately described in the models (exponential PDF in the model against power law in observations [Girard2009]).

Comparison of GlobICE 3-Day (5km resolution) deformation products with coincident RADARSAT RGPS (12.5km) deformation products. Left: GlobICE derived shear component of deformation rate (30/1/2008 to 2/2/2008). Right: RGPS derived shear component of deformation rate (30/1/2008 to 2/2/2008).

Average monthly velocity for September 2010. Prototype GlobICE product for Antarctic sea ice.

Exciting perspectives in preparation for the launch of Sentinel-1

The experience acquired during the GlobICE project at UCL can lead to numerous exciting projects. First the methodology applied to derive the sea ice motion products in the Arctic (mainly from 2008 to 2011) has already been successfully applied to the Antarctic sea ice and prototype products have been generated for the months August and September 2010 (see figure on the left). Excitingly in the Antarctic there is a near total coverage of the sea ice and the processing of the entire ASAR ENVISAT data should provide a novel understanding of the movement of the sea ice around the Antarctic continent. Second the image pair correlation method used to derive ice motion from November to April could also be attempted for the summer season and the months May to October. As sea ice has been melting rapidly over the last decades and is expected to continue to melt in coming decades the feasibility of this project needs to be established if reliable 'summer like' sea ice motion products can continue to be produced in the future. Finally the much anticipated launch of ESA's sentinel-1 in 2013 or 2014 will provide increased coverage of the sea ice cover both spatially and temporally. The CPOM both at UCL and MSSL will undoubtedly contribute significantly to the processing and scientific analysis of these new data.

References

[Kwok1990] [doi] R. Kwok, J. C. Curlander, R. McConnell, and S. S. Pang, "An ice-motion tracking system at the alaska sar facility," Oceanic engineering, ieee journal of, vol. 15, iss. 1, pp. 44-54, 1990.
[Bibtex]
@ARTICLE{Kwok1990,
author = {Kwok, R. and Curlander, J.C. and McConnell, R. and Pang, S.S.},
title = {An ice-motion tracking system at the Alaska SAR facility},
journal = {Oceanic Engineering, IEEE Journal of},
year = {1990},
volume = {15},
pages = {44 -54},
number = {1},
month = {jan.},
doi = {10.1109/48.46835},
file = {Kwok1990.pdf:Kwok1990.pdf:PDF},
issn = {0364-9059},
keywords = {Alaska SAR facility;Canadian RADARSAT;European ERS-1;Japanese ERS-1;algorithm;area-based
techniques;automated analysis;automatic selection;computerised signal
processing;feature based technique;geophysical processing system;ice
floes;ice-motion;ice-motion estimator;ice-motion tracking;image pairs;image
sequences;matching routines;remote sensing satellites;rotation;synthetic
aperture radar;tracking;translation;computerised signal processing;geophysics
computing;oceanographic techniques;radar applications;radar measurement;remote
sensing;sea ice;tracking systems;}
}
[Rampal2011] P. Rampal, J. Weiss, C. Dubois, and J. -M. Campin, "Ipcc climate models do not capture arctic sea ice drift acceleration: consequences in terms of projected sea ice thinning and decline," J. geophys. res., vol. 116, p. C00D07--, 2011.
[Bibtex]
@ARTICLE{Rampal2011,
author = {Rampal, P. and Weiss, J. and Dubois, C. and Campin, J.-M.},
title = {IPCC climate models do not capture Arctic sea ice drift acceleration:
Consequences in terms of projected sea ice thinning and decline},
journal = {J. Geophys. Res.},
year = {2011},
volume = {116},
pages = {C00D07--},
month = sep,
abstract = {IPCC climate models underestimate the decrease of the Arctic sea ice
extent. The recent Arctic sea ice decline is also characterized by
a rapid thinning and by an increase of sea ice kinematics (velocities
and deformation rates), with both processes being coupled through
positive feedbacks. In this study we show that IPCC climate models
underestimate the observed thinning trend by a factor of almost 4
on average and fail to capture the associated accelerated motion.
The coupling between the ice state (thickness and concentration)
and ice velocity is unexpectedly weak in most models. In particular,
sea ice drifts faster during the months when it is thick and packed
than when it is thin, contrary to what is observed; also models with
larger long-term thinning trends do not show higher drift acceleration.
This weak coupling behavior (1) suggests that the positive feedbacks
mentioned above are underestimated and (2) can partly explain the
models' underestimation of the recent sea ice area, thickness, and
velocity trends. Due partly to this weak coupling, ice export does
not play an important role in the simulated negative balance of Arctic
sea ice mass between 1950 and 2050. If we assume a positive trend
on ice speeds at straits equivalent to the one observed since 1979
within the Arctic basin, first-order estimations give shrinking and
thinning trends that become significantly closer to the observations.},
file = {Rampal2011.pdf:Rampal2011.pdf:PDF},
issn = {0148-0227},
keywords = {Arctic, IPCC climate models, decline, kinematics, sea-ice, 0750 Cryosphere:
Sea ice (4540), 0762 Cryosphere: Mass balance (1218, 1223), 0798
Cryosphere: Modeling (1952, 4316), 1626 Global Change: Global climate
models (3337, 4928)},
owner = {mct},
publisher = {AGU},
timestamp = {2012.01.29},
url = {http://dx.doi.org/10.1029/2011JC007110}
}
[Girard2009] [doi] L. Girard, J. Weiss, J. Molines, B. Barnier, and S. Bouillon, "Evaluation of high-resolution sea ice models on the basis of statistical and scaling properties of arctic sea ice drift and deformation," Journal of geophysical research-oceans, vol. 114, iss. C8, p. C08015, 2009.
[Bibtex]
@ARTICLE{Girard2009,
author = {Girard, L. and Weiss, J. and Molines, JM and Barnier, B. and Bouillon,
S.},
title = {Evaluation of high-resolution sea ice models on the basis of statistical
and scaling properties of Arctic sea ice drift and deformation},
journal = {Journal of Geophysical Research-Oceans},
year = {2009},
volume = {114},
pages = {C08015},
number = {C8},
doi = {10.1029/2008JC005182.},
file = {Girard2009.pdf:Girard2009.pdf:PDF},
publisher = {American Geophysical Union}
}